@c Copyright (C) 1996, 1997 John W. Eaton
@c This is part of the Octave manual.
@c For copying conditions, see the file gpl.texi.

@node Strings
@chapter Strings
@cindex strings
@cindex character strings
@opindex "
@opindex '

A @dfn{string constant} consists of a sequence of characters enclosed in
either double-quote or single-quote marks.  For example, both of the
following expressions

@example
@group
"parrot"
'parrot'
@end group
@end example

@noindent
represent the string whose contents are @samp{parrot}.  Strings in
Octave can be of any length.

Since the single-quote mark is also used for the transpose operator
(@pxref{Arithmetic Ops}) but double-quote marks have no other purpose in
Octave, it is best to use double-quote marks to denote strings.

@c XXX FIXME XXX -- this is probably pretty confusing.

@cindex escape sequence notation
Some characters cannot be included literally in a string constant.  You
represent them instead with @dfn{escape sequences}, which are character
sequences beginning with a backslash (@samp{\}).

One use of an escape sequence is to include a double-quote
(single-quote) character in a string constant that has been defined
using double-quote (single-quote) marks.  Since a plain double-quote
would end the string, you must use @samp{\"} to represent a single
double-quote character as a part of the string.  The backslash character
itself is another character that cannot be included normally.  You must
write @samp{\\} to put one backslash in the string.  Thus, the string
whose contents are the two characters @samp{"\} may be written
@code{"\"\\"} or @code{'"\\'}.  Similarly, the string whose contents are
the two characters @samp{'\} may be written @code{'\'\\'} or @code{"'\\"}.

Another use of backslash is to represent unprintable characters
such as newline.  While there is nothing to stop you from writing most
of these characters directly in a string constant, they may look ugly.

Here is a table of all the escape sequences used in Octave.  They are
the same as those used in the C programming language.

@table @code
@item \\
Represents a literal backslash, @samp{\}.

@item \"
Represents a literal double-quote character, @samp{"}.

@item \'
Represents a literal single-quote character, @samp{'}.

@item \0
Represents the ``nul'' character, control-@@, ASCII code 0.

@item \a
Represents the ``alert'' character, control-g, ASCII code 7.

@item \b
Represents a backspace, control-h, ASCII code 8.

@item \f
Represents a formfeed, control-l, ASCII code 12.

@item \n
Represents a newline, control-j, ASCII code 10.

@item \r
Represents a carriage return, control-m, ASCII code 13.

@item \t
Represents a horizontal tab, control-i, ASCII code 9.

@item \v
Represents a vertical tab, control-k, ASCII code 11.

@c We don't do octal or hex this way yet.
@c
@c @item \@var{nnn}
@c Represents the octal value @var{nnn}, where @var{nnn} are one to three
@c digits between 0 and 7.  For example, the code for the ASCII ESC
@c (escape) character is @samp{\033}.@refill
@c 
@c @item \x@var{hh}@dots{}
@c Represents the hexadecimal value @var{hh}, where @var{hh} are hexadecimal
@c digits (@samp{0} through @samp{9} and either @samp{A} through @samp{F} or
@c @samp{a} through @samp{f}).  Like the same construct in @sc{ansi} C,
@c the escape 
@c sequence continues until the first non-hexadecimal digit is seen.  However,
@c using more than two hexadecimal digits produces undefined results.  (The
@c @samp{\x} escape sequence is not allowed in @sc{posix} @code{awk}.)@refill
@end table

Strings may be concatenated using the notation for defining matrices.
For example, the expression

@example
[ "foo" , "bar" , "baz" ]
@end example

@noindent
produces the string whose contents are @samp{foobarbaz}.  @xref{Numeric
Data Types}, for more information about creating matrices.

@menu
* Creating Strings::            
* Searching and Replacing::     
* String Conversions::          
* Character Class Functions::   
@end menu

@node Creating Strings
@section Creating Strings

@DOCSTRING(blanks)

@DOCSTRING(char)

@DOCSTRING(int2str)

@DOCSTRING(com2str)

@DOCSTRING(strcat)

@DOCSTRING(string_fill_char)

@DOCSTRING(str2mat)

@DOCSTRING(ischar)

@DOCSTRING(isstr)

@node Searching and Replacing
@section Searching and Replacing

@DOCSTRING(deblank)

@DOCSTRING(findstr)

@DOCSTRING(index)

@DOCSTRING(rindex)

@DOCSTRING(split)

@DOCSTRING(strcmp)

@DOCSTRING(strrep)

@DOCSTRING(substr)

@node String Conversions
@section String Conversions

@DOCSTRING(bin2dec)

@DOCSTRING(dec2bin)

@DOCSTRING(dec2hex)

@DOCSTRING(hex2dec)

@DOCSTRING(dec2base)

@DOCSTRING(base2dec)

@DOCSTRING(strjust)

@DOCSTRING(str2num)

@DOCSTRING(toascii)

@DOCSTRING(tolower)

@DOCSTRING(toupper)

@DOCSTRING(do_string_escapes)

@DOCSTRING(undo_string_escapes)

@DOCSTRING(warn_num_to_str)

@DOCSTRING(warn_str_to_num)

@DOCSTRING(warn_single_quote_string)

@node Character Class Functions
@section Character Class Functions

Octave also provides the following character class test functions
patterned after the functions in the standard C library.  They all
operate on string arrays and return matrices of zeros and ones.
Elements that are nonzero indicate that the condition was true for the
corresponding character in the string array.  For example,

@example
@group
isalpha ("!Q@@WERT^Y&")
     @result{} [ 0, 1, 0, 1, 1, 1, 1, 0, 1, 0 ]
@end group
@end example

@DOCSTRING(isalnum)

@DOCSTRING(isalpha)

@DOCSTRING(isascii)

@DOCSTRING(iscntrl)

@DOCSTRING(isdigit)

@DOCSTRING(isgraph)

@DOCSTRING(islower)

@DOCSTRING(isprint)

@DOCSTRING(ispunct)

@DOCSTRING(isspace)

@DOCSTRING(isupper)

@DOCSTRING(isxdigit)
